The BGS Lexicon of Named Rock Units — Result Details

Teirw Siltstone Formation

Computer Code: TSI Preferred Map Code: TSI
Status Code: Pending Upgrade
Age range: Soudleyan Substage (OY) — Soudleyan Substage (OY)
Lithological Description: Grey, thinly laminated to pervasively bioturbated siltstones and interbedded mudstones, with local massive, lenticular sandstones and channelised intraformational mudstone conglomerates and a localised tuff member, the Pen Bwlch Tuff.
Definition of Lower Boundary: Conformably overlies rocks of the Swch Gorge Tuff Formation (qv).
Definition of Upper Boundary: Conformably overlain by rocks of the Pandy Tuff Formation (qv).
Thickness: 210 to 250m
Geographical Limits: Not defined.
Parent Unit: Not Available (!)
Previous Name(s): Teirw Beds [Obsolete Name And Code: Use TSI] (TWB)
Alternative Name(s): none recorded or not applicable
Stratotypes:
none recorded or not applicable
Reference(s):
Brenchley, P J, 1978. The Caradocian rocks of the North and West Berwyn Hills. Geological Journal, Vol.13, 137-164. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E120 E137